Despite active research on high-density optical disks in recent years, there has still been a problem that high-density recording is difficult to be carried out due to the fact that uniform recording is prevented by the change in size of record marks as caused by a change in recording light quantity of a light beam projected on an optical disk or by a change in recording magnetic field strength of an externally applied magnetic field applied on a magneto-optical disk.
As a method for solving this problem, a control method of recording light quantity as disclosed in Japanese Unexamined Patent Publication No. 16965/1997 (Tokukaihei 9-16965) has been available. This method is adopted in a so-called light modulation recording device which records data by turning on or off a light beam, and optimizes the recording light quantity during the on state. The following will describe the above method referring to FIG. 12.
First, in FIG. 12, record marks 102 are recorded on a track 101. When the recording light quantity is increased, the record marks elongate, as indicated by the broken line. This changes a duty ratio, which is the ratio of a record mark 102 to a portion (non-record mark) 103 other than the record mark 102. The change in duty ratio appears as a change in read signal so that a read signal 104a as indicated by the solid line is changed to a read signal 104b as indicated by the broken line. The change in duty ratio is detected with ease by detecting the DC components of these read signals. Further, when record marks are recorded beforehand by a plurality of different recording light quantities in a predetermined range, by searching a duty ratio of 1 to 1 from these record marks, it is possible to determine the optimum recording light quantity, which is the recording light quantity at which the duty ratio is 1 to 1.
However, when the control of recording light quantity is carried out on a disk with a small heat capacity by the described conventional method, a problem is presented that the optical disk is heated excessively by the maximum light quantity in a predetermined range of the recording light quantity and the optical disk is destroyed by the heat. The same problem is also presented when the environment temperature is high, whereby the optical disk is excessively heated by the maximum light quantity and the disk is destroyed by the heat.